Gurdas Singh’s wife was cheating on him and he knew it. “You somehow sense it, especially if you’ve been in a long marriage,” Singh, a businessman in Rohini, a posh Delhi suburb, told me over the phone. Last year, Singh, who had been married for eight years, decided to have her followed. The person he hired for the job was Bhavna Paliwal, Delhi’s self-anointed “commander of detectives”. A week later, Paliwal called Singh to say that his wife was in a shopping mall with a man who was almost certainly her lover. High drama followed when Singh caught them red-handed, says Paliwal: “There was fighting, crying, you name it.” The man had flown in from South Africa for a date with Singh’s wife. She had met him on Facebook.

Paliwal, 38, is Delhi’s most famous private detective. She’s also the most colourful. A large-set woman with a round, cheerful face, she dresses in striped shirts and fitted trousers, her long hair lined with fiery-red sindoor. She wears a diamond pin in her nose and a diamond pendant around her neck. If she isn’t talking, she’s laughing, long and hard, at her own stories, all of which she narrates in a tone of high amusement.

There is no lack of stories. Paliwal has been in the business for 15 years. She came to Delhi from a village in Uttar Pradesh in her early 20s; attended college and then started work as a journalist. In a year, she had moved on to a detective agency.

“I lied to my family about what I exactly did. They thought I had a desk job. It was working fine, and then my photographs began to appear in the papers. My family found out I was actually investigating cases in the field,” Paliwal says, pressing the silent button on one of the three mobile phones lined up on her desk.

In 2003, she started her own outfit, Tejas Detective Agency, in the middle of a giddy maze of office buildings in Pitampura, north Delhi. No name or number is evident outside. Private investigation is technically illegal in India, and working from unidentified locations is common. It’s a small office with two rooms, a narrow reception space and a kitchen, all divided by low wooden partitions. Paliwal sits behind a desk one could at best call functional: computer, mobile phones, files, notebooks. On a wooden shelf behind her is a copy of the law book Kanoon Coverage.

Paliwal offers the services private detectives thrive on all over the world: investigating financial frauds, missing persons and, in the words of Mma Precious Ramotswe of The No 1 Ladies’ Detective agency, “husbands carrying on with the ladies”. It’s this last that has been crucial to Paliwal’s dramatic rise in an industry growing at a manic pace (there are some 3,500 private detective agencies in Delhi alone). She lords it over matrimonial investigations. “I get three to four calls a day, sometimes more,” she says. The rate for a prematrimonial assignment – discovering the details of “salary, character, family status, and, if it’s a man, whether he drinks, smokes, gambles” – ranges from 50,000 to 150,000 rupees (£510-£1,530). The rate for cases involving married couples depends on the nature of the job, and can run into millions of rupees.

In other words, Paliwal’s success as a matrimonial detective is directly proportional to the failure of urban Indian marriage. She’s quick to point out a game-changing factor, though: “Earlier, the cheating was one-sided. Now it’s two-sided.” The culprit, she says, is technology: “Most people who come to me have been married for eight to 10 years. Their marriages were going fine, but they started copying youngsters and got into the habit of Facebook, WhatsApp. Many of them go too far into it, ruining their families.”

When clients come to her with suspicions about their partners, she makes sure to tell them that if they had bothered to arrange a prematrimonial investigation (or “premat”), they wouldn’t be sitting across from her now. “If you go for premat, you won’t need postmat,” Paliwal says with a shrug. She’s glad, however, that there is more demand for “premat work” than ever before. “Matches are being made through newspaper ads, matrimonial websites, even social networking websites, so it becomes very important,” she says.

Often, it’s not parents who approach her but young people who are being set up. “There was one boy recently, he had found someone through newspaper classifieds. The girl was well-educated and had a very successful business. They were from similar castes also.” The boy and the girl met each other, Paliwal says, and became very close in no time. “But just before the wedding, the boy began to feel a little doubt: ‘Why is this person marrying me? I am shorter than her and earn nothing in comparison.’ He called me.” It took Paliwal a month of work, which included tracing the girl’s history and having her followed. “What do I find – the business actually belongs to the girl’s boyfriend, a married man. He can’t leave his wife because her family has stakes in his business, so he has taken a house for the girlfriend and put her up there. Now the girl’s family in her village had come to know of all this and were very upset, therefore she needed to get married in order to keep her arrangement going.”

There were a handful of female detectives working in Delhi when Paliwal started out, but now women are a dominant presence. A basic internet search for female detectives in Delhi throws up a glut of agencies. Most stress the point with dubiously sourced photographs of women in overcoats, hats and dark glasses, with binoculars. All the female detectives I meet suggest that women have an edge over men in investigating matters of the heart. “We female detectives deliver the best in personal problems, as we understand human nature better,” reads the Why Us section of ladydetectivesindia.com.

Akriti Khatri, the 28-year-old head of Venus Detective in the predominantly Punjabi district of Preet Vihar, says all she has to do is show up between 1–2pm at the venue of her investigation. “Most premat work I do involves Punjabi households, and Punjabi aunties are at their most free and most desperate for a chat at that time of the day, with nothing to do between eating lunch and cooking dinner. They will tell you anything.

“I would knock at the house of the guy whose credentials I have to investigate for marriage,” says Khatri, sitting in an office surrounded by coaching institutes and computer repair shops. “His mother would open the door, I would ask her if they had advertised for paying guest services, she would say no. But by that time I would already have entered the living room.”

Khatri would ask the mother if any other houses in the area were taking in lodgers. While she searched her memory, the woman would ask Khatri if she wanted water or tea. Khatri would accept and “as she makes tea, I start asking her questions disguised as small talk – How many children do you have, auntie? When do they come home in the evening? Oh, your son works the night shift? Is he often late coming home? And so on.”

As Khatri teases out information she walks around the living room, a hidden camera in her bag recording the family’s possessions, from the make of the television set to the number of air conditioners. Those would later be matched against the material status the family had claimed in front of its prospective in-laws.

Khatri is a fresh-faced, sharp-featured woman who could pass as a college student if she weren’t sitting behind an imposing semi-circular desk. She has been on the job for nearly 10 years, starting after college. “I did take a break and went and did an MBA course and got a sales job. But then I thought I could make so much more money doing detective work and I would enjoy the job, so I came back to the agency where I had started,” she says, fiddling with the long sleeves of her red tunic. She grew up in a Punjabi family in east Delhi, has worked extensively in the area, and knows its every little secret.

Most of her work now comes from the corporate world. “I get a call from this guy, at a senior level in a big company. He tells me, I am having an affair with an employee, a married woman. I am calling you because I think she is having another affair, and I want you to find who the man is,” says Khatri, throwing me a can-you-believe-it look.

Lady Detectives India website

Sometimes she asks her clients to come to her, having effectively done their homework for them. “Now you can just go online or to your neighbourhood market and buy spyware.” There are specialised markets for spy equipment in Delhi where one can buy binoculars or GPS trackers. There are India-focused websites that tout hundreds of varieties of spy cameras – actionindia.in advertises cameras hidden in pens, watches, belts, spectacles, pendants, car keys, and even, bizarrely, in handwash dispensers, chewing gum and water flasks.

Khatri sometimes sells a little metal chip to clients that she says can take care of most of their worries: “You fit it inside the cellphone of the person you are targeting. I give you an email and password and you can track everything they do via the phone – calls, texts, WhatsApp, Facebook, the photos they take, the videos they record. It even tracks their physical movements.”

But she says she no longer wants to take up cases her clients can solve themselves: “I am not doing this for money any more.” Last year, she married one of her team members, and recently became a mother.

On most days, Khatri considers her job to be straightforward – sitting in an office and supervising people – but she knows things can turn crazy in an instant. “This morning, for example, I started getting calls from 5am. A man asked me to follow a girl, an actress, who is supposed to arrive at Hyderabad airport at 5.30am, and tell him where she goes. My guys are all over the airport – at the arrival concourse, the taxi point, the pick-up point for private vehicles. They are calling me every few minutes with updates. I’ve no option but to catch sleep between phone calls. If the man I’m paid to follow leaves a bar at 1.30am, I can go to bed only after that. That’s understood.”

It wasn’t until a few years into the job that she realised holidays meant peak work time for private detectives who specialised in cheating partners. “From October to January – the entire festival season – it’s hard for us to find people to delegate work. Every person in the field is booked weeks in advance,” she says. It’s the time of year when people watch their partners most closely. “Last year, I got a call from someone during Christmas week. He tells me: ‘My girlfriend is going to be with me on the 24th, but she is claiming to be busy on the 25th. Can you follow her?’”

Twenty years of experience ... Taralika Lahiri, head of National Detectives and Corporate Consultants in New Delhi. Photograph: Vikram Sharma/IndiaTodayImages

I heard a similar argument from Taralika Lahiri, the 54-year-old director of National Detectives and Corporate Consultants, a team of 15 investigators working from an office in Khirki Extension, one of Delhi’s urban villages. Lahiri, who got her first assignment, a murder case in rural Haryana, 20 years ago, doesn’t need to get her hands dirty any more, unless it’s something that requires experience.

“There was this case where a woman wanted proof of her husband’s cheating. All she told me was that on his last vacation, he had gone on an adventure sports tour with his girlfriend,” she says. “I found out what travel agency he had used to book the tour and went straight to its manager. I made up a story about having been on the same tour. I convinced him enough to get out of him all the booking and payment records, including the number of the hotel room where he had stayed with his mistress.”

We meet at her home office in Panchsheel, an upscale, tree-lined Delhi colony, where she sits in a tall black leather chair in a room decorated with her trophies and framed certificates. “It’s a man’s world and you have to push your way through,” she says when I press her about the challenges of being a woman in her line of work. When she joined a detective agency in Delhi at the age of 24, it wasn’t even as an investigator. “Only men used to do this job. I had joined in the marketing division. And then one day they had a banking fraud case in Allahabad to solve, and I came from a family of bankers in Allahabad, so they put me on the job. There was no looking back.” She stood out, she says, in just a few years. “You know they used to say in the field that Taralika will do in two days what a man will take 10 days to do,” she says, smiling for the first time since I walked in.

Does their work make them cynical about marriage? None admit to it, but all the female detectives I speak to say they continue to be surprised by the games partners played in relationships. “The case that really blew me away was of this woman who said she knew her husband was having an affair, and she just wanted me to give her the evidence,” says Khatri. “So I ask her what she will do with it – bring it up with their families, or go to the court? She told me she would do neither – she would save the evidence for when she is caught cheating.”